In a printing photomechanical process for the graphic arts, the formation of sharp dot images or line images is required and hence an image-forming system showing very high-contrast photographic characteristics (in particular, 10 or higher in gamma) is necessary. Hitherto, for the purpose, a lith-type silver halide photographic material having a silver halide emulsion layer composed of a silver chlorobromide emulsion having a silver chloride content of more than 50%, and preferably more than 70% with a lith developer (lithographic developer) having a very low free sulfite ion concentration (usually, not higher than 0.1 mol/liter) has been used.
However, since for a lith-type silver halide photographic emulsion, a silver chlorobromide emulsion having a high silver chloride content must be used, it is difficult to attain a high sensitivity.
As other processes for obtaining high-contrast negative images, there are processes of using specific hydrazine derivatives disclosed in U.S. Pat. Nos. 4,168,977 4,224,401, 4,241,164, 4,269,929, 4,311,781, 4,650,746, 4,927,734, etc.
According to these processes, by processing surface latent image type silver halide photographic materials each containing a specific hydrazine derivative (generally, an acylphenylhydrazine derivative) as a nucleating agent with a developer having pH of from 11.0 to 12.3, photographic characteristics having a super high contrast of over 10 in gamma are obtained. According to these processes, a silver bromide emulsion or a silver chlorobromide emulsion having a high silver bromide content can be used, thereby a high sensitivity can be attained as compared with the case of using a lith-type silver halide emulsion.
However, it has been found that the foregoing high-contrast image-forming system using acylhydrazine derivative has various disadvantages. That is, the use of the foregoing image-forming system can give high-contrast negative images but at the same time is accompanied by the formation of pepper (black spot), which causes a serious problem in the photomechanical process. The pepper means black sesame-like spots formed at none-image area, i.e., undeveloped portions among dots, which causes serious damage on the commercial value of the light-sensitive materials for photomechanical process. Accordingly, various efforts have been made for developing a pepper-restraining technique but the attempt of restraining the formation of pepper is frequently accompanied by lowering the sensitivity and gamma. Thus, the development of an image-forming system for attaining a high sensitivity and a high contrast without accompanied by the formation of pepper has been strongly desired.
A second disadvantage of the conventional high-contrast image-forming systems is that a large amount of hydroquinone which is expensive and becomes a material causing an environmental pollution must be used for keeping the activity of the developer constant.
A lith developer is easily air-oxidized owing to a low sulfite ion concentration in the developer to greatly consume hydroquinone which is the developing agent.
Also, the developer for the high-contrast image-forming system using a hydrazinc derivative is allowed to contain a sulfite at a high concentration but the developer is liable to be air-oxidized owing to the high pH (from 11 to 12.3) to greatly consume hydroquinone. Therefore, for keeping the developing activity of these developers, it is necessary to keep the amount of hydroquinone in the developer above a definite level by using a large amount of hydroquinone which is expensive and becomes a material causing an environmental pollution as described above or by replenishing the amount of hydroquinone consumed by the air-oxidation. Thus, the development of a high-contrast image-forming system by a developer causing less consumption of hydroquinone or without using hydroquinone as the developing agent has been desired.